Optical discs, such as compact discs (CDs) and digital versatile discs (DVDs), are a form of computer-readable media that provide storage for digital information. Some optical discs may be read-only, while others may also be written to. Typically, one side of an optical disc is referred to as a data side, while the other side is referred to as a label side. The label side may include label text and/or graphics.
An optical disc drive is used to read from and, in some cases, to write to the data side of an optical disc. An optical pickup unit is included in the optical disc drive and is configured with a laser and sensors for reading from and writing to the data side. An optical pickup unit may also be configured for writing to the label side. However, writing to the label side may involve defocusing the laser (or offsetting the laser lens from the “best” focus point) to decrease labeling times. For example, a mark having about the same contrast can be printed at a faster speed by moving the lens closer to the disc than “best” focus. Problems with using focus offset include uncertainty in laser power and uncertainty in the electrical-to-mechanical gain of the focus actuator that positions the lens.